Method for attaching a torque measuring device

ABSTRACT

In a method for fastening a torque measurement device ( 4 ) for detecting a relative torque between an input shaft ( 2 ) and an output shaft ( 3 ) of a steering system ( 1 ), in particular of a rack-and-pinion power-assisted steering system, the torque measurement device ( 4 ) is integrally formed locally into the input shaft ( 2 ) and/or the output shaft ( 3 ) by means of deformation elements ( 8 ).

[0001] The invention relates to a method for fastening a torque measurement device for detecting a relative torque between an input shaft and an output shaft. The invention also relates to an input shaft and/or output shaft for carrying out the method.

[0002] In steering systems, in particular in power-assisted steering systems, in which manual steering is assisted by an electric motor, an exact, reliable and permanent detection of a relative torque between an input shaft and an output shaft is particularly important for ascertaining the steering requirement. The torque measurement device used for detection is in this case generally installed between an input shaft, which is connected to a steering spindle connection, and an output shaft, which is connected to a pinion. The torque measurement device thus detects the relative torque between the steering spindle connection or input shaft and the pinion or output shaft and controls the drive of an electric motor via an electronic module. The electric motor may in this case serve for the power assistance of the conventional steering apparatus.

[0003] As regards the operating principle of a rack-and-pinion power-assisted steering system, reference is made, in this regard, to EP 0 366 691 B1.

[0004] A method, known from practice, for fastening a torque measurement device to an input shaft and an output shaft of a steering system provides, in this context, for the torque measurement device to be welded to the input shaft and the output shaft. It became clear in this case, however, that this welded joint is complicated and not sufficiently reliable. A break of the weld seam may occur, for example, when the wrong material is welded. Since the torque measurement device is a safety-relevant element which is to operate with high precision and reliably, the fastening method must satisfy particularly stringent demands and possibilities of error must be ruled out as far as possible.

[0005] The object on which the present invention is based is to overcome the disadvantages of the prior art, in particular to provide a method of the type initially mentioned, which allows an accurate, reliable and permanent fastening of a torque measurement device between an input shaft and an output shaft of a steering system and can be carried out in a favorable and simple way and which largely rules out error sources which may lead to a release of the connection.

[0006] This object is achieved, according to the invention, by means of the characterizing part of claim 1.

[0007] Since the torque measurement device is integrally formed locally into the input shaft and/or the output shaft by means of deformation elements, a reliable, permanent and exact connection is obtained, which virtually rules out an inadvertent release of the torque measurement device, for example due to the choice of wrong material. Moreover, the method can be carried out simply, quickly and cost-effectively. It is also advantageous in this case, as tests have shown, that the connection is corrosion-proof, vibration-proof, temperature-resistant and resistant to physical influences.

[0008] The connection made by the method according to the invention has, moreover, particularly high strength. As tests have likewise shown, the torque measurement device can be fastened exactly in the intended position.

[0009] It is advantageous, at the same time, that even materials which cannot be welded to one another can be connected. A choice of the materials to be processed which is determined by welding criteria may therefore be dispensed with. According to the method, fastening can also be carried out particularly cost-effectively because round parts can be connected to one another without any previous form fit.

[0010] An adverse heating of the components involved during the assembly process or contamination, such as has occurred relatively frequently in the method known from the prior art, is reliably prevented by means of the method according to the invention. Furthermore, there is no need to use further additional connection elements, such as, for example, pins, clips or the like.

[0011] An unexpected secondary effect of the fastening of the torque measurement device to the input shaft or the output shaft which can be carried out reliably in terms of the process is advantageously that, if appropriate, even repeated connection, particularly with regard to hardened shafts, and therefore reuse are possible.

[0012] As tests have shown, the torque measurement device can advantageously be connected, free of play, to the input shaft or output shaft, so that it is possible, for example by means of an electric motor, to assist the predetermined steering requirement exactly and in a simple way.

[0013] Furthermore, according to the invention, there may be provision for the torque measurement device to have a magnetic ring and a sensor which are integrally formed into the input shaft or the output shaft by means of the deformation elements.

[0014] By the torque measurement device being designed with a magnetic ring, which can be fastened to an input shaft, and with a sensor for fastening to an output shaft, the relative torque between the input shaft and the output shaft can be picked up in a particularly simple way. The torque and, from this, the necessary assisting force provided by the electric motor can be determined with the aid of other parameters from the angular rotation which is ascertained.

[0015] It is advantageous if the input shaft and/or the output shaft are/is provided with reception points for receiving the material of the torque measurement device which is to be integrally formed locally and if the reception points are designed as depressions, countersinks, bores or the like.

[0016] By means of the reception points in the input shaft and/or the output shaft, the torque measurement device or the magnetic ring and/or the sensor can be fastened to the input shaft or to the output shaft in a simple way. This results in a form-fitting connection which arises from a form-fitting and frictional assembly operation. In-this case, it is sufficient if one of the two parts to be connected, in this case the input shaft and/or the output shaft, has, before the assembly operation, the possibility of the subsequent form fit.

[0017] Fastening the torque measurement device according to the method can be carried out with particularly little effort, exactly, quickly and permanently by means of the reception points. Flexibility in the mounting or setting of the torque measurement device is not influenced in the least in this case, since the torque measurement device is designed without a previous form fit and can therefore be oriented or attached in any desired way. Only after an appropriate actuation of the deformation elements, which integrally forms the material of the torque measurement device locally into the reception points, is there the desired permanent and reliable connection between the torque measurement device and the input or output shaft.

[0018] The force of the deformation elements which is to be applied for connection is reduced substantially by means of the reception points, with the result that it is possible to adhere to the intended position particularly accurately.

[0019] In one embodiment of the invention, there may be provision for the torque measurement device to be integrally formed by means of a deep-drawing process.

[0020] An embodiment of this type has proved to be particularly reliable in terms of the process and to be simple to carry out.

[0021] It is advantageous if, for integral forming, three deformation elements designed as deformation rams are provided and the number and position of the reception points and of the deformation rams are adapted to one another.

[0022] As tests have shown, by the deformation elements being designed with three deformation rams and by correspondingly adapted reception points, a secure and reliable fastening of the torque measurement device is possible, which, furthermore, can be carried out quickly and cost-effectively. It is advantageous, for this purpose, if the reception points are introduced into the shaft so as to be offset in each case at 120°.

[0023] In a structural embodiment of the connection, there may be provision for the integral forming of the torque measurement device to be checked by means of force/path monitoring.

[0024] By means of force monitoring, a connection which is particularly reliable in terms of the process is possible, since, for example, metal sheets which are too thin or material defects are detected due to the lower resistance. Furthermore, the path monitoring ensures that, even when increased resistance occurs, the metal sheet is introduced into the reception points in the intended way or, if the intended path distance is not reached, the part is not freed.

[0025] An advantageous input shaft and/or output shaft for carrying out the method may be gathered from claim 16.

[0026] Advantageous refinements and developments of the invention may be gathered from the further subclaims and from the exemplary embodiment illustrated below, in principle, with reference to the drawing in which:

[0027]FIG. 1 shows a section through a torque measurement device which is integrally formed into an input shaft and an output shaft of a steering system;

[0028]FIG. 2 shows a view in the direction of the arrow II of FIG. 1; and

[0029]FIG. 3 shows an enlarged illustration of a magnetic ring which is arranged on a sheet-metal ring and which is caulked with the input shaft.

[0030]FIG. 1 shows part of a steering system 1, in particular of a rack-and-pinion power-assisted steering system, with essentially an input shaft 2, an output shaft 3 and a torque measurement device 4.

[0031] The input shaft 2 is in this case connected, in a way not illustrated, via a steering spindle connection to a steering handle for transmitting a steering requirement. The output shaft 3 forms, in a way not illustrated in any more detail, a drive pinion which is in engagement with a rack in the usual way. The rack is connected in a known way to steerable wheels via a steering linkage.

[0032] As is evident from FIG. 1, the torque measurement device 4 is fastened or installed both on the input shaft 2 and on the output shaft 3. The torque measurement device 4 can thus detect a relative torque between the input shaft 2 and the output shaft 3 or between the steering spindle connection and the drive pinion. By means of the relative torque which is detected, an electric motor is controlled via an electronic module, not illustrated.

[0033] As can be seen in FIG. 1, the torque measurement device 4 has a magnetic ring 5 and a sensor 6. In the exemplary embodiment illustrated, the magnetic ring 5 is arranged on a cylindrical sheet-metal ring 7 which, according to the method, is integrally formed locally into the input shaft 2 by means of deformation elements 8 indicated merely in principle (see FIG. 3). In a similar way to this, the sensor 6 is arranged on a holding plate 9 by means of spiral springs 10 and is integrally formed into the output shaft 3 by means of the deformation elements 8.

[0034] An arrangement of the magnetic ring 5 on the input shaft 2 and of the sensor 6 on the output shaft 3 has proved particularly advantageous for measuring the angle of rotation between the input shaft 2 and the output shaft 3. In an alternative embodiment, of course, there may also be provision for the arrangement of the magnetic ring 5 and of the sensor 6 to be reversed.

[0035] As is customary in hydraulic steering systems, the input shaft 2 and the output shaft 3 are connected to a torsion bar 11. The torque can thus be calculated via the torsion bar rigidity and the measured angle of rotation.

[0036] A particularly advantageous arrangement of the sensor 6 with the holding plate 9 in relation to the magnetic ring 5 with the cylindrical sheet-metal ring 7 may be gathered from FIG. 2.

[0037] For advantageous integral forming of the holding plate 9 into the output shaft 3 or for the local integral forming of the cylindrical sheet-metal ring 7 into the input shaft 2, reception points 12 can be seen in the output shaft 3 (FIG. 1) and in the input shaft 2 (FIG. 3). The reception points may be designed as depressions, countersinks or, advantageously, as bores 12 and advantageously receive the material of the torque measurement device 4 which is to be integrally formed locally. An inadvertent displacement or juddering of the torque measurement device 4 set or oriented exactly before deformation is thus largely reduced.

[0038] A particularly advantageous integral forming of the cylindrical sheet-metal ring 7 or the holding plate 9 into the input shaft 2 or the output shaft 3 is possible, using three deformation elements which are arranged correspondingly uniformly around the input shaft 2 or the output shaft 3. A design of the deformation elements as deformation rams 8 is advantageous. The number and position of the bores 12 may in this case be adapted in a simple way to the deformation rams 8. The input shaft 2 and the output shaft 3 which are illustrated in the exemplary embodiment consequently in each case have, in a way not illustrated in any more detail, three bores 12 which are arranged in each case so as to be offset at 120°.

[0039] It has proved advantageous if the bores 12 are designed as cylindrical bores with countersinks. A bore diameter of 1 to 4 mm, preferably 2 to 3 mm, a bore depth of 1 to 3 mm, preferably 1.5 to 2 mm, a countersink at 45° and a countersink depth of preferably 0.5 to 1 mm have proved particularly suitable in tests with regard to rapid, cost-effective, accurate and permanent integral forming. As has been shown, the edge between the countersink and the cylindrical part of the bore 12 is responsible for advantageous freedom from play. A large part of the holding forces is likewise transmitted via this edge. As tests have shown, a 10% clearance in the bore depth is particularly advantageous for ensuring the material flow.

[0040] As regards the bore 12, care must be taken to ensure that the bore onset is not sharp-edged. The countersink advantageously makes it possible that the material of the cylindrical sheet-metal ring 7 or the holding plate 9, said material being deep-drawn into the bore 12, is not sheared off. The local integral forming of the material of the cylindrical sheet-metal ring 7 or of the holding plate 9 according to the method can be checked by means of force/path monitoring. A deep-drawing process has proved particularly suitable for integral forming.

[0041]FIG. 3 shows an advantageous fastening of the magnetic ring 5 to the input shaft 2 and of the sensor 6 to the output shaft 3 which has been carried out by means of the method according to the invention.

[0042] That part of a steering system 1 which is illustrated in FIG. 1 and FIG. 2 conventionally has, in addition to the components already described, a worm 13, a bearing 14 and a connecting pin 15 which connects the torsion bar 11 to the input shaft 2.

[0043] The functioning of the worm 13 and of the bearing 14 are sufficiently known and play no part in the method according to the invention, so that a more detailed description is dispensed with.

[0044] The use of a spiral spring 10 is already known, in principle, from airbag technology, and therefore a more detailed description is likewise dispensed with. The spiral spring 10 may be provided with the ribs 10 a, illustrated in FIG. 2, for protection against rotation.

[0045] In principle, it is not necessary to use a spiral spring 10 for signal transmission, and other methods, for example contactless transmission methods, may also be used for this purpose.

[0046] There are likewise various measurement principles known, by means of which an angle of rotation between a magnetic ring 5 and a sensor 6 can be determined or detected, and therefore these are not discussed in any more detail, especially because the measurement principle for the method according to the invention is not of any major importance.

[0047] A particularly advantageous version of the method provides, in a first method step, for aligning the deformation rams 8 and the bores 12 with one another. This ensures that the deformation rams 8 and the bores 12 are correctly aligned with one another. Subsequent mutual alignment, particularly when the torque measurement device 4 is already positioned, is thus avoided and, consequently, an unintentional displacement of the torque measurement device 4 is prevented.

[0048] The deformation rams 8 therefore advance first, without the torque measurement device 4 being arranged, in the direction of the input shaft 2 or the output shaft 3, are aligned with the bores 12 and subsequently move back again.

[0049] In a second method step, the holding plate 9 having the sensor 6 is applied to the output shaft 3 and is integrally formed locally into the bores 12 of the output shaft 3 by means of the deformation rams 8. Since the holding plate 9 is a round part without a previous form fit, it can be applied to the output shaft 3 in a simple way. A positioning exact to a hundred percent is not absolutely necessary in this case.

[0050] The sensor 6 may, of course, also be applied to the input shaft 2 in the way described. In a further alternative embodiment, in which, of course, the following method steps have to be adapted correspondingly, there may also be provision first for fastening the magnetic ring 5 with its cylindrical sheet-metal ring 7 to the input shaft 2 or the output shaft 3 and subsequently for positioning and fastening the sensor 6 in relation to the magnetic ring 5.

[0051] In a third method step, the deformation rams 8 are then applied to the not yet occupied or still free reception points. This takes place, in principle, in a similar way to the first method step already described. For this purpose, depending on the embodiment, either the same deformation rams 8 or another unit of deformation rams 8 may be used.

[0052] In a fourth method step, after the fastening of the sensor 6, the cylindrical sheet-metal ring 7 together with the magnetic ring 5 is applied to the input shaft 2 and is set or positioned in relation to the sensor 6 fixed in the second method step.

[0053] In a fifth method step, the cylindrical sheet-metal ring 7 together with the magnetic ring 5, positioned in the fourth method step, is integrally formed into the bores 12 of the input shaft 2 by means of the deformation rams 8. After the integral forming process, the deformation rams 8 can be drawn back again.

[0054] The fastening according to the method gives rise to a permanent connection of the torque measurement device 4 to the input shaft 2 or the output shaft 3, said connection being reliable in terms of the process. The method according to the invention can be used for materials currently available in this sector, in particular for sheet steel, sheet brass and VA sheet. The use of sheet brass or VA sheet as materials has particular advantages by virtue of the corrosion resistance.

[0055] By means of the method described, magnets can also be fastened to a worm. The magnet then serves, here, for detecting the rotational speed of a motor and does not have to be set.

[0056] Reference Symbols

[0057]1 Part of a steering system

[0058]2 Input shaft

[0059]3 Output shaft

[0060]4 Torque measurement device

[0061]5 Magnetic ring

[0062]6 Sensor

[0063]7 Cylindrical sheet-metal ring

[0064]8 Deformation element

[0065]9 Holding plate

[0066]10 Spiral spring

[0067]10 a Ribs for protection against rotation

[0068]11 Torsion bar

[0069]12 Reception points/bores

[0070]13 Worm

[0071]14 Bearing

[0072]15 Connecting pin 

1. A method for fastening a torque measurement device for detecting a relative torque between an input shaft and an output shaft of a steering system, in particular of a rack-and-pinion power-assisted steering system, characterized in that the torque measurement device (4) is integrally formed locally into the input shaft (2) and/or the output shaft (3) by means of deformation elements (8).
 2. The method as claimed in claim 1, characterized in that the torque measurement device (4) has a magnetic ring (5) and a sensor (6) which are integrally formed into the input shaft (2) or the output shaft (3) by means of the deformation elements (8).
 3. The method as claimed in claim 2, characterized in that the magnetic ring (5) is arranged on a cylindrical sheet-metal ring (7) and the cylindrical sheet-metal ring (7) is integrally formed into the input shaft (2) by means of the deformation elements (8).
 4. The method as claimed in claim 2 or 3, characterized in that the sensor (6) is arranged on a holding plate (9) by means of a spiral spring (10) and the holding plate (9) is integrally formed into the output shaft (3) by means of the deformation elements (8).
 5. The method as claimed in one of claims 1 to 4, characterized in that the input shaft (2) and/or the output shaft (3) are/is provided with reception points (12) for receiving the material of the torque measurement device (4) to be integrally formed locally.
 6. The method as claimed in claim 5, characterized in that the reception points (12) are designed as depressions, countersinks, bores or the like.
 7. The method as claimed in claim 5 or 6, characterized in that, in a first method step, the deformation elements (8) and the reception points (12) are aligned with one another.
 8. The method as claimed in claim 7, characterized in that, in a second method step, the sheet-metal ring (7) together with the magnetic ring (5) or the holding plate (9) together with the sensor (6) is integrally formed into the reception points (12) of the input shaft (2) or the reception points (12) of the output shaft (3) by means of the deformation elements (8).
 9. The method as claimed in claim 6 or 7, characterized in that, in a third method step, the deformation elements (8) are aligned with the still unoccupied reception points (12).
 10. The method as claimed in claim 8 or 9, characterized in that, in a fourth method step, the sheet-metal ring (7) together with the magnetic ring (5) or the holding plate (9) together with the sensor (6) is applied to the input shaft (2) or the output shaft (3) and is set or positioned in relation to the magnetic ring (5) or to the sensor (6) fixed in the second method step.
 11. The method as claimed in one of claims 7 to 10, characterized in that, in a fifth method step, the sheet-metal ring (7) together with the magnetic ring (5) or the holding plate (9) together with the sensor (6), positioned in the fourth method step, is integrally formed into the reception points (12) of the input shaft (2) or of the output shaft (3) by means of the deformation elements (8).
 12. The method as claimed in one of claims 1 to 11, characterized in that the torque measurement device (4) is integrally formed by means of a deep-drawing process.
 13. The method as claimed in one of claims 1 to 12, characterized in that, for integral forming, three deformation elements designed as deformation rams (8) are provided.
 14. The method as claimed in claim 13, characterized in that the number and position of the reception points (12) and of the deformation rams (8) are adapted to one another.
 15. The method as claimed in one of claims 1 to 14, characterized in that integral forming of the torque measurement device (4) is checked by means of force/path monitoring.
 16. An input shaft and/or output shaft for carrying out the method as claimed in one of claims 1 to 15, characterized in that the input shaft (2) and/or output shaft (3) have/has reception points (12) for receiving the material of the torque measurement device (4) which is to be integrally formed.
 17. The input shaft and/or output shaft as claimed in claim 16, characterized in that the reception points (12) are designed as a countersink, depression, bore or the like.
 18. The input shaft and/or output shaft as claimed in claim 17, characterized in that three cylindrical bores (12) offset in each case at 120° and having countersinks are provided.
 19. The input shaft and/or output shaft as claimed in claim 17 or 18, characterized in that the bore diameter is 1 to 4 mm, preferably 2 to 3 mm, the bore depth is 1 to 3 mm, preferably 1.5 to 2 mm, the countersink is at 45° and the countersink depth is preferably 0.5 mm to 1 mm. 